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Discussion Starter · #1 ·
Hello,

I have a 1987 mustang gt, and not to long ago I had problems with what I thought was my
Fuel pump. When I drove the car and did WOT after 3000rpm the power would drop.

So I replaced my fuel pump and put in a Walbro 255lph fuel pump. The cars power had improved
For sure. It wouldn't bog down anymore after 3000rpm, but it doesn't have the power, the pull it
Once had?? Like before first gear at WOT the back end would swing out, not anymore? What could be the problem?? I had replace my tps aswell and the timing is at 13deg. What kind of fuel should I put in?

I don't know anymore any info would be awesome and helpful. Oh I did check my fuel pressure with the new pump, and idle its at 38-39PSI and with the fuel pressure regulator vacuum off its at like 45-48PSI. And it stays the same while driving.

I would like my power back..! My diesel jetta drives better! Any help

Thanks a lot!
 

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Factory exhaust?

If it still has the factory cats on it they may be stopping up with carbon. Have you noticed a change in temperature of the engine or a change in the exhaust note? If the exahust is free flowing look at fuel metering for your problem.Like O2 sensors etc.I run high octane fuel in pony's myself.
 

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other than checking the 02's or cats, when was the last time it got a good tune up?
 

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Discussion Starter · #4 ·
Thanks for the input guys! First, no I don't have cats I have bbk shorty headers with H-pipes and flowmasters, the O2 sensors have not been changed ever as far as I now,

As for a tune up I believe at least 3 years since it had one, the only thing I changed as far as tune up is the spark plugs to autolites 25 (I have 1970 GT40 351W heads with B303 cams)

Which spark plugs do you suggest?

Also I have been thinking to upgrade to a MSD distributor and MSD box for awhile now, would that benefit me in anyway?

Would there be anything else I should be looking at that might fix this issue?

Thanks again
 

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Take what I have to say with a grain of salt, and if my reasoning is wrong please correct me but if by you changing fuel pumps made the car run better but still not like it use to I would next check the fuel filter, then the injectors. It should still be possible to show good fuel pressure with a clogged injector right? And same with a clogged fuel pump? Or maybe one of the injector O-rings is busted?

Is there any stumbling or hesitation at all, or just no get up and go?

I hope you get the problem figured out:bigthumbsup
 

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I had an issue not too long ago where I thought my pump was going out. It would run ok but if I would "gun" it, it would bog down when I would hit 3800-4k rpm. I knew for sure it was the fuel pump so I replaced it with a 255. Come to find out I had a very tiny, almost minute burn mark on one of my plug wires. I swithched out the plugs and wires and that completely fixed her.
 

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Discussion Starter · #7 ·
Good and interesting points. Thanks,

When I changed the fuel pump the filter was changed aswell, and the pump filter is new, the gas tank is new aswell was changed like 2 years back.

The injectors could be bad? Or even my fuel pressure regulator?
I would have to look into my injectors too see how they're doing. Check the voltage there getting.

As far as the wires that's very interesting, ill have to take a look at them and see if there is any damage to them. Like I said before I should do a tune up on the car anyway.

What spark plugs should I run on my heads? I have 1970 351W GT40 heads, I'm currently running autolite 25.

If I do my tune up should I consider to upgrade to an MSD system? Distributor and A6L?
 

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I dont know anything about MSD or 351 heads so I cant help you out there. I bet once you replace the wires and plugs its gonna run good for ya.

When I was trying to figure out which plugs to run on my gt40P the majority of advice was to look up what stock plugs were run in them and go with that.

I dont know if these are the same heads as yours or not. But he is running autolite 764.

spark plug gap on autolite 764 for GT40 irons? - Ford Mustang Forums : Corral.net Mustang Forum


I just had an issue yesterday where I changed out a set of manifolds for a buddy. When I test drove it it would sputter just a tad bit every great once in a while when I would give it gas to accelerate. His plug wires were stock, it was a 2001 v6 stang with 130,000 miles. I dont know whats on the inside of the wires but I must have broke a few of the fibers by yankin em out by the wire instead of the boot. I replaced the wires and now it runs like a top.
 

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How can you have 1970 GT40 heads...what is their casting number?
 

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Discussion Starter · #10 ·
I'm sorry if that's the incorrect info on the heads that's what I was told when I bought the car, but I didn't really think they had GT40's back then? I will have to take a look at the cast number and get back to you with more info on that.

I know for sure they were from a 351W the heads have had a lot of work done on them from rockers to cams, ported and shaved to the max.

But yeah again ill look at the number.


Does anyone think upgrading to MSD is worth it? Should I grab the msd distributor and A6L box? Or should I just do a basic tune up?

Also would a bad battery/weak alternator cause problems with loss of power and pull?? I do believe I'm due for both.
 

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Discussion Starter · #11 ·
hello everyone,

I test drove my mustang and I played around with the timing. now I got my power but it would come and go, it would pull hard in first then as soon as I shift into second it almost feels like its lagging at first and then it get half the power it should?

I'm not sure whats going on with the car, like I'm ready to just do a full rebuild or sell it.

still haven't had the car running great yet its making me angry ha.

and thoughts??

thanks.
 

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I've also had this problem with my car. When I fist got the car it would take off pretty good and after about a yr or so my clutch cable broke and since I didn't know much mechanics the car sat for about 3 months and ever since the car hasn't ran the same. That was about 4yrs ago and now I know my way around my car and just can't seem to figure out what has caused such power loss I've changed the fuel filter,spark plugs,wires,etc. I'm starting to think it might be my injectors.
 

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Discussion Starter · #13 ·
soo the update is, I talked to a bunch of people and a lot of them are telling me to check my injectors? and also that I should be running bigger injectors with the heads I have. I have 19lb injectors right now.

what are your thoughts on this?
 
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